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Alpha-N with MAP comp.....and BARO?

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Application is naturally aspirated. Either ITBs or plenum type intake with a big cam (low MAP).

Main fuel table Alpha-N. MAP sensor and FPR referenced to the intake manifold (manifold log in the case of ITBs).

TPS indicates load. MAP indicates density of air the engine consumes. FPR referenced to intake maintains a constant delta pressure across the injectors to simplify the injector offset Calc.

The question is....would there be a benefit from also having BARO comp?

Depends on the ECU and driving conditions.

Some ECU's will sample the MAP sensor on start up and use that value as the Baro pressure and compensate off of that value. This works well in most circumstances. What can cause an issue is if you start the engine at sea level, or close to it, and then drive into the mountains without stopping the engine/cycling the ECU. The MAP sensor should still be compensating as you will be running in a different area of the map (as long as it has been tuned correctly) but the Baro compensation may have an effect on the fueling as its stored value is different to the actual value.

Nigel,

I run an ITB setup on a big block Ford. The ECU is setup with Alpha-N and MAP compensation. I have also configured it with a second sensor for BARO compensation. Did this for the exact reason that BlackRex pointed out. Some of the cruises we have done had an elevation change over 8,000 ft. Did this without shutting the engine down and it ran perfectly from top to bottom. The guys who were carb'd had all kinds of issues. The guys with the normal ECU setup would drive till they had issues, then pull over, stop the engine then restart. Most ECU's will default to a barometric pressure at time of startup.

If your routes are all the same elevation, not necessary, but if you like to run the big hills, it's recommended.

Paul

Thanks guys. Running Motec M800 so able to do live BARO comp in addition to MAP comp.

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